1. Field of the Invention
This invention relates to the field of detecting the presence or proximity of metal elements, objects or articles, more particularly ferromagnetic materials, and more specifically in an industrial environment.
The invention has more particularly as its object a device for detecting metal plate elements, more particularly a so-called double sheet detection device, as well as a system for selecting and transferring such elements.
2. Description of the Related Art
During the production of sheet metal parts, the latter are brought near the station for cutting, stamping, folding or the like, in the form of stacked flat elements.
They must then be selected one at a time to be brought toward or into the processing station, or onto a conveyor belt of such a station.
At this time, it should be guaranteed that the sheets are brought individually to prevent any malfunctioning or stopping of the processing station that can be caused by the simultaneous processing of two or more stacked sheets.
To remove this risk, various devices for detecting metal plate elements, such as metal sheets or plates, intended in particular to work with or to be incorporated into a system for selection, movement, transfer and/or positioning or the like of such elements, have already been proposed.
Thus, by the document DE 3505671, a device for measuring the thickness of a sheet by determining the change in the inductance of an electromagnet is known, and by the document DE 3425354, a device for measuring the thickness of a sheet by using Foucault currents is known, by determining a differential voltage between the voltage recovered at the terminals of a detection coil and a reference voltage.
The processes used in these documents are complex and are based on the evaluation and the interpretation of the value of an absolute analog measurement, whence uncertain reliability results. Moreover, no constructive embodiment of a material device is disclosed by these documents.
By the document DE 298 08 830, a device to mark metal parts is known, this device comprising emission and reception coils that can be positioned between one another according to different configurations.
By the document US 2001/0020846, a position sensor to determine the location of a metal element in relation to a group of emission and reception coils that are inclined in relation to one another is known.
However, neither of these two known devices uses the amplitude of the signal collected, nor all the more makes it possible to determine the number of detected parts or elements.
Moreover, so-called “double sheet” detection devices are known that each consist mainly, on the one hand, of an emitting coil supplied by suitable control means and generating a magnetic field; on the other hand, of a reception or receiving coil placed so as to make possible the generation by induction of a voltage at the terminals of said coil under the action of the aforementioned magnetic field, and, finally, of means for processing and evaluating the voltage signal provided by said at least one reception coil, making it possible to provide an informative signal indicating the absence or the presence of one or more metal elements in the vicinity of said coils.
In these double sheet detectors that are known and used in particular within the framework of automobile construction, the sheet or the edge of the sheet must necessarily be put through the gap between the two coils, the latter being placed opposite.
This constraint slows down the movement of the manipulated sheets and necessitates a precise positioning, with a movement along an additional path, indeed a specific monitoring station at the level of the supply means of the station or of the machine for processing said sheets.
Furthermore, these known double sheet detectors with opposite coils exhibit a considerable bulk.